Axial flow compressor cooling system



April 24, 1951 s. A. KANE 2,549,819

AXIAL FLOW COMPRESSOR COOLING SYSTEM Filed Dec. 22, 1948 2 Sheets-Sheet 1 INVENTOR.

Saul Allan Kcme Attorney April 24, 1951 s, A, KAN 2,549,819

AXIAL FLOW COMPRESSOR COOLING SYSTEM Filed Dec. 22, 1948 2 Sheets-Sheet 2 F IG.3. FIG.4.

6 G E B E a if D m (D u F Lu 2 a: m n.

VOLUME PRESSURE INVENTOR.

Soul Allan Kane Attorney Patented Apr. 24, 1951 AXIAL FLOW COIMPRESSOR COOLING SYSTEM Saul Allan Kane, Washington, D. 0.

Application December 22, 1948, Serial No. 66,693

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) 1 Claim.

The present invention relates to a compressor cooling system and more particularly to axialflow compressors using water cooling.

It is well-known by those skilled in the art that the adiabatic compression of air elevates the temperature of the compressed air to high values. In axial-flow compressors, the friction and wind age losses of the machines also heat the air in addition to the heat resulting from the adiabatic compression of the air, with the net result that a several hundred degree temperature difference exists between the inlet and discharge ends of the machine. The temperature increase produced in an axial-flow compressor increases the amount of energy required to produce a particular weight of air at a desired pressure, and it is the weight of air rather than the volume which governs the size and efficiency of the installation. It can be shown mathematically that a compressor having a 5:1 ratio and an efiiciency of 80% produces a temperature rise of 392 F. and that a compressor having a 7 :1 ratio produces a temperature rise of 554 F. with an efficiency of 75%. The increased temperature of the air resulting from changing the compression ratio from 5:1 to 7:1 causes a reduction in efiiciency in the neighborhood of 5%. It is probable that future development of the gas turbine will result in higher compression ratios and, since the temperature rise increases exponentially as the compression ratio increases, in greatly increased temperature rises with correspondingly reduced efiiciencies.

It has been found to be diificult to carry off this heat in the air by cooling the compressor itself by means of water passages because of the high velocity of the air. The use of intercoolers between stages of the compressor results in additional fluid frictional losses, and because intercoolcrs are heavy and bulky, results in greatly increased size of the installation.

The present invention is directed to removing the heat from the air undergoing compression. while it is being compressed by injecting sprays of a cooling liquid into air axial flow compressor in small quantities at a number of points so as to absorb the heat by evaporation of the cooling liquid into vapor.

It is an object of the present invention to provide an axial-flow air compressor which is efiectively cooled during compression without the addition of intercoolers. I

It is a further object of the present invention to provide an axial-flow air compressor which is cooled by the evaporation of a cooling liquid throughout the air passages.

A still further object of the present invention is to provide an axial-flow air compressor which is provided with means for injecting a spray of a cooling liquid into a plurality of stages of the compressor.

Further objects and advantages of the present invention will be apparent by reference to the description and to the annexed figures in which:

Fig. 1 is a longitudinal sectional view of an axial-flow compressor;

Fig. 2 is a cross-section of the compressor taken on the line 2-2 of Fig. 1;

Fig. 3 is a temperature-pressure chart showing the adiabatic compression curve and the compression curve of the present invention;

Fig. 4 is a pressure-volume chart showing the comparison of the isothermal compression cycle, the adiabatic cycle. and the compression cycle of the present invention;

Fig. 5 shows one form of nozzle suitable for use with the present invention; and

Fig. 6 shows a special compressor blade which may be used as a nozzle in connection with the present invention.

Referring now to Fig, 1, the casing H of the compressor is supported by suitable supports l2. It will be understood that the type of mounting used to support the machine will vary with the individual installation, and the arrangement shown is intended to be merely illustrative. The casing H is tapered from a large diamcter at the intake end to a considerably smaller diameter at the discharge end. The inside of the casing is adapted to receive a number of inwardly projecting radial blades l3 which are arranged in spaced rings perpendicular to the longitudinal axis of the casing. A flared inlet throat M is attached to the intake end of the casing to reduce turbulence and improve the operation of the machine. An intake manifold could be employed if it is desired to connect the intake to a conduit and since the design of such an intake manifold is old and well known to those skilled in the art, it is not illustrated. Any desired type of discharge manifold may be employed and attached to the discharge end of the machine as by the flange l8 shown. Since these components are not a part of the invention, they will not be described in detail.

Within the casing I I is a rotor l5 supported coaxially with the casing by means of the shaft I6. Bearings of suitable type must be provided to support the rotor in correct alignment and to absorb the axial thrust produced by the machine, but since bearings of suitable types are well known to those skilled in the art, and since they form no part of the present invention, they are not shown or further described.

As shown, the rotor 15 is conical and tapers from at larger diameter at the inlet end to a smaller diameter at the discharge end. While the rotor I5 and the casing H are both tapered in the same direction, the angle between the surface of the casing and its axis is larger than the angle between the surface of the rotor and its axis, and hence, the radial distance between the inside of the casing and the outside of the rotor decreases toward the discharge end of the compressor.

Attached to the circumference of the rotor i5 are a plurality of radial outwardly extending blades H which are arranged in parallel rings about the longitudinal axis of the rotor in suitable position to intersperse between the several rings of stationary blades [3. The stationary blades is are of such length as to extend nearly to the surface of the rotor and to leave a small clearance to allow for expansion and contraction of the parts. The rotary blades 11 extend nearly to the inside surface of the casing II, with only a small clearance, and the clearance between stationary and adjacent rotary blades is made very small to reduce the size of the machine and to improve its operation. The arrangement of the blading and the cross-section of the individual blade are conventional and well known in the art. As is well known, the stationary blades are pitched relative to the air flow in the opposite sense to the pitch of the ratary blades, but since the blading forms no part of the present invention, it is not further described.

Openings are provided at a plurality of points spaced about the casing II to receive nozzles 21 which nozzles are connected to each other and to an inlet 22 for the cooling liquid by means of piping 23 which is arranged to provide a uniform distribution of the cooling agent to the several nozzles and may be of any desired design. Alternately, passages may be formed in the casing wall to conduct the liquid from the inlet 22 to the nozzles 2|. The nozzles 2| are distributed about the periphery of the casing II to obtain a substantially equal peripheral distribution of water and are located at longitudinal points at which the air is heated sufficiently to evaporate the cooling agent quickly. The evaporation process, of course cools the air and the compressor at the injection area but when the cooling agent is completely evaporated, the further compression again raises the temperature of the mixture of the air and vapor and additional nozzles are placed at each location where cooling is desirable to maintain a nearly constant air temperature.

The cooling liquid used with the axial-flow compressor will depend upon the type of installation and its location. In most cases the medium employed will be water, but in extremely cold climates and in aircraft, it will be necessary to use a liquid having a low freezin point, such as water mixed with alcohol, but it may also be desirable to employ liquids having boiling points other than that of water in certain installations. The term cooling liquid as used in this application is intended to cover any liquid which may be used for cooling by evaporation.

Figure 5 shows a cross-section of a type of nozzle which may be used to inject the cooling liquid into the compressor as a fine spray. The nozzle consists of an open-ended shell 24 which screws into the casing H at suitable locations. Inside the shell is a deflector 25 supported by a spider 26 attached to the shell in a position to receive the impact of the cooling liquid entering the shell 24 through the piping 23, the impact forming a fine spray which enters the compressor through the open end of the shell.

Fig. 6 shows a modification of a nozzie suitable for use with the present invention. Since the stationary blades are not subject to centrifugal force, they are not required to withstand high stresses and it is evident that such a blade may contain a cavity while maintaining adequate strength. The blade 36 is attached to casing II by conventional means and contains a suitable cavity 3! which extends substantially the length 'of the blade, and may be of any convenient crosssection and series of passages 32 extend from the cavity 3!, to the forward edge of the blade 30. The cooling agent piping 23 is connected to the cavity by any suitable means, as for example, by means of an opening in the casing H adjacent the root of the blade and in a position to connect with the cavity 3|, whereby coating agent entering the cavity flows through the passages 32, and is diffused by impact with the high velocity air passing around the blade, forming a fine spray. The heat of the air causes the spray to be converted to a vapor, thus cooling the air. This form of nozzle provides the advantage of a more even dis 'ribution of Water within the compressor because water is injected near the surface of the rotor as well as the surface of the casing.

It will be evident to those skilled in the art that the form of the nozzle employed or the type of axial-ilow compressor may :be varied to meet the requirements of the particular installation.

The operation of the present system of cooling may be readily understood by reference to Fig. 3, which indicates the temperature rise of air passing through an axial-flow compressor. The curve 35 shows the rise in temperature caused by adiabatic compression where no cooling is used, while the curve 36 shows the efiect of a spray of a cooling agent injected only into the intake of the compressor. It will be noted that the temperature of the air is prevented from raising by evaporation until the cooling agent is completely evaporated, after which the mixture follows the usual adiabatic curve displaced from the curve 35, but since the thermal capacity of the gaseous mixture is raised by the addition of steam, this curve shows a more gradual shape than curve 35. Curve 3? shows the effect of the injection of the cooling agent at a number of points as described in the present disclosure. The temperature of the air is reduced at each injection point by the evaporation of the liquid so that the curve extends downward until the cooling agent is evaporated and then rises again under the influence of compression until the rise in temperature is sufficiently high at which point more cooling liquid is injected causing another dip in the curve, and so on until the mixture has been compressed to the desired pressure and passes out of the compressor. Since the vaporizing temperature of a liquid rises with the increased pressure, the curve 31 has a rising characteristic trend in addition to the heat of compression.

Fig. 4 is a pressure-volume chart in which the area enclosed in the curves represents the work required to produce a given weight of air at a given pressure. The area ABCD represents the work required to produce a desired weight of gas at a given pressure using an adiabatic compressor, while the area AECD represents the work required to produce the same weight of gas at the same pressure with an isothermal compressor, resulting in a reduction in the power requirement which is proportional to the are-a ABEA. An isothermal compression cycle is impossible to achieve in practice.

The cooling system described herein results in a compromise between the two systems above and requires an input proportional to the area AGCD surrounded by the lines AD, CD, BC, and the curve F, which area is considerably less than the area ABCD. It is evident that the increase in efliciency indicated by the difference in area between ABCD and AGCD resulting from the present invention is an important improvement in axial-flow compressors.

It will be apparent to those skilled. in the art that many changes may be made in the present invention without departing from the spirit thereof. Any form of axial-fiowcompressor may be employed, and the number of injection points is a matter of design to determine the desirable positions for such injection points. It should be borne in mind that it is undesirable to inject more of the cooling liquid at any point than can be rapidly evaporated because the excess water will be thrown to the casing wall and cause localized cooling which may cause damage to the compressor by unequal expansion of its parts and the resulting misalignment of parts. The type of nozzle employed is also a matter of design, but should be of a type which will break the cooling liquid into small droplets and disperse it over'a considerable volume in the compressor.

The present inventionis especially applicable to high pressure systems because systems of these types produce very high temperatures which require cooling, and it is particularly applicable where high pressure systems are employed in cramped quarters which do not permit the use of bulky intercoolers.

While water vapor in compressed air is objectionable for some purposes, it is desirable in the case of gas turbines, since the steam has a high thermal'capacity and reduces the turbine temperature while increasing its output by reducing the quantity of gas required to cool the products of combustion before expansion through the turbine. Where the axial-flow compressor is used to supply air to a gas turbine, the cooling liquid can be a mixture of air and a fuel such as alcohol since the temperature is maintained below the flash point of the fuel there is no fire hazard from the heat of compression and the additional fuel avoids leaning out the mixture whenever the quantity of cooling liquid injected in the compression is increased.

It will be obvious to those skilled in the art that the valve 28 may be made automatically responsive to operating conditions if it is desired. An example of such a control is to operate the valve in response to temperature changes in the compressor discharge by means of the pressure of a confined gas subjected to the discharge temperature. Such control systems are well known and may be readily applied by those skilled in the art.

The invention described herein may be manufactured and used by or for the Government of the United States of America for overnmental purposes without the payment of any royalties therefor or thereon.

Having thus described the invention what is claimed is:

An axial flow compressor having a plurality of axially disposed stages of radial blades adapted to successively compress a gas, a, plurality of atomizing nozzles adapted to inject a cooling liquid into selected stages, said selected stages having a plurality of nozzles disposed about its periphery, said selected stages being selectively disposed between others of said sections and means for forcing a cooling liquid through said atomizing nozzles, whereby water is injected at appropriate stages to cool the air passing through said compressor by evaporation of said water.

SAUL ALLAN KANE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,400,813 Graemiger Dec. 20, 1921 1,751,537 Vianello Mar. 25, 1930 2,280,845 Parker Apr. 28, 1942 2,406,126 Zweifel s Aug. 20, 1946 

